1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
During normal ambulation, the first part of a foot to contact the ground is the free end of the heel. This initial contact between heel and ground is known as the xe2x80x9cheel strike.xe2x80x9d The free end of the heel is soft and thus cushions the heel strike to at least some extent. The hard bottom of the heel is the next part of the foot to strike the ground; its hardness allows it to support the entire weight of the body. The foot continues to rotate in the well-known way until the toes xe2x80x9cpush offxe2x80x9d at the end of a step.
Early prosthetic feet were quite rigid and provided little or no cushion to the impact on the ground at the moment of xe2x80x9cheel strikexe2x80x9d and little or no elastic response at xe2x80x9cpush off.xe2x80x9d The shock of impact was thus transmitted directly to the skeletal structure of the user, and the lack of elastic response forced an unnatural gait.
Perhaps the earliest prosthetic foot that provided an elastic response at heel strike and push off is disclosed in U.S. Pat. No. 4,547,913 to Phillips, assigned to Flex Foot, Inc. Multiple versions of that device have been developed. The original version is formed of a carbon fiber epoxy matrix consisting of a one-piece combination pylon upper and a one-piece sole. Mechanical fasteners interconnect the upper and the sole. In a second embodiment, the pylon is a round hollow tube and is connected by mechanical fasteners to a rectangular-shaped upper. A third version is like the first except that a standard Sach(copyright) foot adapter is employed to connect a standard prosthetic pylon. A fourth version is like the third but has a slightly different geometry. In a fifth version, an elastomeric glue connects the upper and the sole. In additional embodiments, leaf springs or hydraulic cylinders are incorporated into the prosthetic foot.
Although the developments in the art since the mid 1980s have significantly advanced the technology of prosthetic feet, the known prosthetic feet still provide little or no heel elasticity in a direction parallel to the ground. Instead, they provide elastic response in a vertical plane. Thus, although the impact at heel strike is reduced vis a vis the pre-1980""s prosthetic feet, the reduced impact is transmitted vertically to the skeletal structure of the user, and the elastic response in a vertical plane-causes a four to six millimeter bounce at heel strike. This vertical response causes an unnatural walk because a healthy human heel is soft at the back or free end where heel strike occurs and is hard on the bottom so that it can support the entire weight of the body. Thus, the normal gait of a human includes a rolling motion as the back of the heel strikes the ground; there is no vertical motion causing the heel to bounce upon ground impact. Accordingly, there remains a need for a prosthetic foot that provides substantial heel elasticity in a direction parallel to the ground.
A healthy human foot rolls on the lateral part of the foot during ambulation. The medial part of the foot provides a cushion and the force required at push off. Thus, there is a smooth transition from heel strike to push off, with no vertical dynamic response of the type that could cause the foot to bounce. Prosthetic feet of the type heretofore known, however, do not provide a smooth transition from heel strike to push off. This lack of a smooth transition produces what is known in the industry as a xe2x80x9cflat spot.xe2x80x9d The presence of a flat spot between heel strike and push off produces an unnatural gait.
More particularly, the dynamic response is primarily vertical at the heel and the toe of a prosthetic foot. There is little or no component of the dynamic response in a horizontal plane as present in a healthy natural foot. The absence of dynamic response in a horizontal plane results in a step like motion going from an elastic vertical motion at heel strike to little or no support at mid-stance (the flat spot), and then again to an elastic vertical motion at push off.
There is a need, therefore, for a prosthetic foot having a dynamic response in a horizontal plane during heel strike, that provides a smooth transition between heel strike and push off to eliminate the flat spot, and that provides a dynamic response in a horizontal plane during push off.
The human foot provides a more rigid support laterally than medially. This design is advantageous because when an instability occurs, the weight of the person shifts from the rigid outer or lateral edge of the foot to the less, rigid inner or medial edge. In this way, the prosthetic foot takes advantage of the presence of the natural foot, i.e., the lateral-to-medial motion experienced at the moment of an instability shifts additional support duties to the natural foot. One major drawback of the heretofore known prosthetic feet is the fact that such feet provide an exactly vertical response during ambulation with no component toward the medial section of the foot. Thus, if an instability in one foot urges the person to fall away from the natural foot, there is no shift of weight toward the medial part of the prosthetic foot as would occur in a natural foot, and the likelihood of a fall is substantially increased.
A prosthetic foot is therefore needed that has differentiated medial and lateral stiffness so that it can respond to instabilities in much the same way as a natural foot.
The single pylon structures of the prior art also exhibit a relatively high torsional stiffness.
Accordingly, there is a need for an improved prosthetic foot that exhibits a lower torsional stiffness when compared to the prosthetic feet of the prior art.
Early prosthetic feet also have a poor rollover motion. Thus there is a need for a prosthetic foot having an improved rollover motion.
Yet another drawback of early prosthetic feet is that they include surfaces that wear against one another, making unwanted noises and wearing out at an accelerated pace.
There is a need, therefore, for a prosthetic foot that has no surfaces that rub against one another, thereby producing a substantially noise-free foot having increased durability.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The long-standing but heretofore unfulfilled need for a dynamic prosthetic foot is now met by a new, useful, and nonobvious dynamic prosthetic foot having multiple load points and a single upper. The novel foot includes a sole having a heel end and a toe end that are in substantially coplanar relation to one another.
An upper member having a heel end and a toe end overlies the sole. The heel end of the upper member has a gradual ninety degree bend formed therein. The heel end of the upper member separates from the sole along a parting line that is transverse to a longitudinal axis of the prosthetic foot.
A slot is formed in the heel end of the upper member. The slot is substantially coincident with the longitudinal axis of the prosthetic foot and the slot extends from an uppermost end of the heel end of the upper member to a preselected point in the gradual ninety degree bend. The slot divides the heel end into a pair of flat, transversely spaced apart, pylon supports. The pylon supports, including a lateral pylon support and a medial pylon support, are disposed substantially perpendicular to the sole.
A lateral pylon connector adapted to receive a lateral pylon of a prosthetic leg is secured to a trailing end of the lateral pylon support. A medial pylon connector adapted to receive a medial pylon of a prosthetic leg is secured to a trailing end of the medial pylon support. Accordingly, forces acting on the lateral pylon connector are substantially confined to the lateral section of the upper member and forces acting on the medial pylon connector are substantially confined to the medial section of the upper member.
The lateral pylon support has a greater thickness than the medial pylon and the medial section of the upper member. The greater thickness imparts greater stiffness so that forces applied to the lateral pylon support and the medial pylon support are transferred more to the medial pylon support and the medial section of the upper member than to the lateral pylon support and the lateral section of the upper member, thereby mimicking the reaction of a natural foot to forces applied thereto.
Forces acting on the lateral pylon support are therefore transferred at least in part to the medial pylon support and forces acting on the medial pylon support are substantially confined to the medial pylon support.
The sole has a first convexity formed in the heel end that performs the function of the bottom of a natural heel. The sole has a concavity longitudinally spaced from the first convexity, said concavity performing the function of a natural arch. The sole has a second convexity longitudinally spaced from the concavity, said second convexity performing the function of the ball of a natural foot.
The transverse parting line where the heel end of the upper member separates from the sole is positioned substantially in juxtaposition with the bight of the concavity formed in the sole that performs the function of the arch of a natural foot.
In an alternative embodiment, the upper member and sole are integrally formed with one another from said transverse parting line to the toe end of the sole.
In a second embodiment, a pair of elongate pylons that interconnect the prosthetic foot and a prosthetic socket supplants the pylon supports and connectors.
An important object of this invention is to provide a prosthetic foot having heel elasticity in a direction parallel to the ground.
Another important object is to provide a prosthetic foot having a smooth transition from heel strike to push off.
Yet another object is to provide a prosthetic foot having differentiated medial and lateral stiffness so that an instability tends to shift weight from the lateral edge of the prosthetic foot to the medial edge thereof, just as in a natural foot.
Still further objects are to provide a prosthetic foot having medial/lateral stability, torsional flex, and anysotropic stiffness.
Another important object is to provide a prosthetic foot having an improved rollover motion.
Another major object is to provide a prosthetic foot that exhibits lower torsional stiffness than a prosthetic foot having a conventional pylon.
Another object is to achieve the preceding object by providing a prosthetic foot having multiple pylon supports or pylons.
Still another object is to provide a prosthetic foot having no parts that wear against one another, thereby providing a substantially noise-free prosthetic foot having increased durability vis a vis conventional prosthetic feet.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.